Heat oven to 450 degrees. While it's heating up, assemble mushrooms, bell pepper, broccoli, zucchini, and garlic in a large bowl. Toss with olive oil. Mix salt, pepper, & onion powder in a small bowl and then sprinkle over veggies and toss again.
Transfer veggies to a baking sheet and make sure they are spread as much as possible, without overlap or clumping. Pop veggies into the oven. These can roast until the meal is ready to be served.
Meanwhile, heat broth in a medium pot. Bring to a boil. Slowly whisk in cornmeal & rosemary. Once smooth, reduce heat to low, stirring occasionally, for 10 minutes. Once polenta is thick and creamy, remove from heat and stir in butter and cheese.
Serve roasted veggies on top of polenta, next to polenta or mixed into the polenta. I served mine with some arugula greens on the side.
We recommend that all meals for children be served with milk.